The present invention relates to the preparation of wear-resistant hard material layers on a metallic support by applying onto said metallic support a mixture of a hard material, a soldering powder and an organic binding agent (which is thermally decomposable without leaving a residue); burning out said binding agent at a temperature between 300.degree. C. and 500.degree. C. and soldering the particles of said hard material on said support at a temperature between 800.degree. C. and 1100.degree. C.
Currently several techniques are used to protect work pieces from wear, particularly from abrasion. In addition to conventional heat treatment methods (e.g. case hardening, nitration, and boronation), other processes such as thermal spraying and welding and CVD- and PVD-techniques are also used.
According to the process disclosed in DE-OS 31 48 362,wear-resistant layers and solder layers are prepared by spraying a corresponding mixture of metallic powder and wax with the aid of compressed air and subsequently sintering. This process is relatively expensive and is unsuitable for the formation of parts having complicated geometry.
In U.S. Pat. No. 4,749,594, a process for applying hard materials on surfaces is disclosed wherein at first a solder layer and an organic binder and thereafter the hard materials are applied and heated.
According to the process disclosed in U.S. Pat. No. 3,475,161, the object is coated by immersing it into a mixture of the hard material particles, an organic binder and a solvent, and subsequently subjecting the system to sintering. However, this process fails to provide protective layers with optimal effect and good adhesion.
Recently another process has become known, namely the so-called brazecoat technique. According to this process, hard material-solder layers are applied onto the parts subject to wear by placing or sticking on the area to be protected a hard material-solder connecting mat and subjecting this part to a soldering process under a protective gas. The thickness of the layer thus obtained falls generally in the range between 500 and 1500 .mu.m. Such a process is disclosed e.g. in DE-PS 3,801,958.
Pursuant to the above process, formed bodies made of hard materials, soldering powder and organic plastic materials (which can be thermally decomposed without leaving any residue), are applied onto the area to be protected and soldered at a temperature of about 1100.degree. C., whereby the plastic material serving as binding agent is decomposed and forms a hard material layer in a solder matrix on the sites to be protected.
The above mat process has several drawbacks, for example, wear layers below about 500 .mu.m can not be applied by this method. A further disadvantage resides in the fact that the process is limited to parts of simple geometries because complicated mat configurations are difficult to prepare and their application can not be carried out in an automatic manner.